Unless otherwise indicated herein, approaches described in this section are not prior art to the claims listed below and are not admitted as prior art by inclusion in this section.
In wireless communications, channel state information (CSI) refers to information on known channel properties of a communication link having multiple channels. CSI typically describes how a signal propagates from a transmitter (Tx) to a receiver (Rx). CSI also indicates combined effects experienced or suffered by signals transmitted over the communication channels such as, for example, fading, scattering, and power decay. Estimation of CSI, however, can be difficult at times. For example, denoting the communication link as two channels, where one channel is that between base station and the first group of Rx antennas and another channel is that between base station and the second group of Rx antennas, partial channel reciprocity can be considered when the number of transmitters (e.g., one Tx) is less than the number of receivers (e.g., two Rx) at a user equipment (UE).
When there is only one Tx at the UE for transmitting a sounding reference signal (SRS) to the base station without SRS switching, a base station (e.g., gNB or eNB) can only obtain partial information (e.g., information about either of two channels) but not the full channel state information (e.g., information about both of the two channels). In this scenario, regarding CSI acquisition with partial channel reciprocity, only one of the two channels can be estimated by the base station in case that there is no SRS switching. As such, it is difficult for the base station to have correct estimation on noise power at the UE side. Specifically, the base station cannot use channel quality indicator (CQI) derived from full channel state information to derive noise power at the UE side, since one of the two channels is unknown.
Thus, in cases where only partial channel reciprocity is available at the base station, there is a need to allow the base station to effectively obtain full (or almost full) channel state information. Moreover, in cases where only partial channel reciprocity is available at the base station, there is also a need for the ability to identify missing spatial basis to conduct spatial multiplexing transmission.